Gas operated semi-automatic firearm



Nov. l5, 1966 w. E. FowLx-:R

GAS OPERATED SEMI-AUTOMATIC FIREARM 5 Sheets-Sheet 1 Filed Sept. l5, 1964 QQN Nov. 15, 1966 w. E. FowLER GAS OPERATED SEMI-AUTOMATIC FIREARM 5 Sheets-Sheet 2 Filed Sept. l5, 1964 y ZZ/2 V42 Nov. l5, 1966 w. E. FOWLER 3,285,133

GAS OPERATED SEMI-AUTOMATIC FIREARM Filed Sept. l5, 1964 5 Sheets-Sheet 3 WA v .1%

INVENTOR.

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3,285,133 GAS OPERATED SEMI-AUTOMATIC FIREARIVI Walter E. Fowler, 8560 Culfor Crescent, Norfolk, Va. Filed Sept. 15, 1964, Ser. No. 396,676 8 Claims. (Cl. 89-191) This invention relates to a semi-automatic, gas-operated rearm.

The primary object of the invention is the provision of a reliable, simple, and easily taken-down rie ofthe kind indicated, which, while primarily designed for hunting use, is readily convertible to shot-gun and military forms of firearms.

Another object of the invention is the provision of a bolt action ride of the character indicated above which utilizes a staggered box-type magazine and which incorporates safety features, which prevent firing of the rie until and unless the bolt is in locked position, and which prevent movement of the bolt, from retracted position, `while loading the magazine of the rie, either with a single cartridge or a full load of cartridges.

A further object of the invention is the provision, in a rie of the character indicated above, of a gas-operated action which provides smoother, quieter, and less violent, and hence more comfortable, more efficient, and less wear-producing operation of the action, the action being spring-cushioned, and induced by a restrained and controlled use of gas entering an expansion chamber or cylinder, from the ride barrel, the cylinder containing a driving rod or piston.

A still further object of the invention is the provision, in a ride of the character indicated above, of an expansion chamber or cylinder which is carried by the barrel of the rifle, the barrel being removably threaded into the receiver of the rifle, and the barrel assembly being removably connected to the forepart of the stock of the barrel, whereby the barrel assembly can be removed for breech-cleaning thereof, and whereby separately connected components of the action can be reached for cleaning and/or removal.

In the drawings:

FIGURE 1 is a fragmentary and 4contracted vertical longitudinal section taken through a rifle of the present invention, showing the same cocked for firing;

FIGURE 2 is a horizontal section taken on the line 2 2 of FIGURE l;

FIGURE 3 is a view substantially like FIGURE l, showing the components of the rie following firing of the rifle and preceding a loading operation;

FIGURE 4 is a' horizontal section taken on the line 4 4 of FIGURE 3;

FIGURES 5, 6, 7 and 8 are transverse vertical sections taken on the lines 5, 6 6, 7 7 and 8 8, respectively, of FIGURE l;

FIGURE 9 is an enlarged perspective view of the bolt of the rifle, equipped with an extractor; and

FIGURE l0 is an enlarged perspective view of the extractor, per se.

Referring in detail to the drawings, the illustrated rifle comprises a receiver 12, formed with a vertical stagger box cartridge magazine 14 formed with a loading and extraction slot 16, at its upper end, and containing a at horizontal follower plate 18, which is biased upwardly by means of an accordion spring 20, compressed between the follower plate and the floor 22 of the magazine.

The follower plate 18 is formed, on its rear edge, with a projection 24, which, at times, is adapted to engage beneath a shoulder 2.6, on the upper part of a vertical latch rod 28, which is positioned along the forward face of the rear wall 30 of the magazine 14. At its lower ttes arent C 3,285,133 Patented Nov. 15, 1966 ice part, the latch rod 28 slides through the floor 22 of the magazine 14, above which a coil spring 32 is circumposed on the rod, in a recess 34, and acts to bias the rod downwardly, and thereby to extend its lower end 35 below the receiver 12, at a location behind the forepart of a trigger guard 36. This arrangement makes possible and easy the manual raising of the latch rod 28 so that its upper end makes positive stop engagement with the forward end of the bolt of the rifle, in fully retracted position of the bolt, behind the magazine 14, exemplified in FIGURE 3, so that the bolt cannot be accidentally moved forwardly, by the triggerhammer assembly, and block loading of the magazine or injure ngers of the user of the rie, while loading a single cartridge or a full load of cartridges, into the magazine.

The trigger-hammer assembly 38, located within the receiver 12, behind the magazine 14, comprises a hammer 40, having a substantially circular body 42, axially journaled, as indicated at 44, on the receiver, and having a tangential, upwardly extending arm 46. The upper part of the arm 46 is formed with a forwardly facing beveled tiring pin contacting nose 48. The lower part of the hammer body 42 is formed with an arcuate eccentric edge 52, which terminates, at its rear end, in a radial shoulder 54.

A horizontal longitudinal sear 56 works through a bore 58 located on a level below the hammer 40, and is biased rearwardly, by a contractile spring 60. The sear has, on its forward end, an upstanding lug 62, which, inthe firing position of the assembly 38, engages the eccentric edge 52 of the hammer, as shown in FIGURE 1, at a location forwardly of the pivotal axis of the hammer 40. In the cocked position of the assembly 38, shown in FIGURE 3, the lug 62 is engaged behind the shoulder 54 of the hammer 40, and holds the hammer in a rearwardly tilted position, against the resistance of a contractile spring 64, which is stretched between a rearward part of the receiver 12 and a location 66, on the hammer body 42, below and forward of the pivotal axis of the hammer.

The trigger-hammer assembly 38 further comprises a vertical trigger 68, which is pivoted, as indicated at 70, across a recess 72, in the bottom of the receiver, through which the linger-piece 74 of the trigger extends downwardly into the trigger guard 36. The trigger has a V-shaped upper end 76 which is engaged in a V-shaped notch 78 formed in the bottom of the sear S6. A vertical spring 80 is compressed between the top of the recess 72 and the top of a rearwardly extending arm 82 on the trigger, which aids the sear spring 64 in positioning the Sear rearwardly in the bore 58, and angling the trigger finger-piece 74 upwardly and forwardly, in cocked position, as shown in FIGURE 3.

The receiver 12 is formed, above the trigger-hammer assembly 38, with a horizontal bore 84, which opens, at its forward end, into the upper part of the magazine 14, the bore 84 being longer than a bolt 86 which it is adapted to receive, as shown in FIGURE 3, in a retracted position of the bolt. The bolt 86- has a springpressed ejector 87 on its forward end.

The upper part of the receiver 12 forwardly of the magazine 14, is formed with a bore 88, which is aligned with the bore 84, and which, as shown in FIGURES 1,

3, 6 and 7, intermediate its ends, with opposed quarter circular locking grooves 90, adapted to receive Iand release, at different times, a pair of diametrically opposed lugs 92, located adjacent to the forward end 94 of the bolt 86. When the bolt 86 has been moved forwardly, out of the receiver bore 84, and across theA top of the magazine, to receive a cartridge 96 from its magazine and load the cartridge, the lugs 92 enter the locking groove 90, at one end thereof. The forward movement of the bolt is followed by rotation of the bolt, in one direction, so as to position the lugs 92, at the other ends of the grooves 90, whereby the bolt is locked, in ring position. Half bores 89, in the magazine side walls, form effective continua-tions `of the 'bores 84 `and 88.

In this firing position of the bolt 86, its forward end is immediately adjacent to .an annular shoulder 98 which is provided by the rear end of a reduced, externally threaded, reduced diameter boss 102, on the rear end of a rifle barrel 104, having a bore 105 extending to the forward end of the barrel. The barrel bore 105 is formed, :at its rear end, with a cartridge `chamber which comprises a forward annular beveled shoulder 106, and an enlarged diameter rear portion 108 which opens to the rear end of the barrel boss 102. The neck 110 of the cartridge case 112 tits the barrel Ibore 105, and its shoulder 114, conformably engages the chamber shoulder 106, and the rear end 116 of the case 112 extends rearwardly beyond the barrel boss shoulder 98, so as to expose the groove 118 ofthe cartridge case.

A cartridge extractor 120, as shown in FIGURES 9 and l0, comprises a resilient split ring 122, formed, intermediate its ends, with a longitudinal extractor hook 124, extending from one edge of the ring, and with a longitudinal rectangular retainer frame 126 extending from its other edge, in line with the hook. The opening 128 of the frame 126 is proportioned to receive .a locking lug 92, of the bolt 86, with the hook 124 extending forwardly beyond the forward end of the bolt, as shown in FIGURES 9 and l, the extractor ybeing seated ush with the louter surface of the bolt 86. As the ibol-t 86 is pressed forwardly against the rear end of the cartridge 96, in a loading operation, the extractor hook 124 snaps into the cartridge case groove 118, so that after the cartridge has been red and retraction of the bolt 86 takes place, the cartridge is pulled rearwardly out of the cartridge chamber, and is ejected by the ejector 87.

The above mentioned rotation of the bolt 86, between locked yand unlocked positions, is in part produced by the engagement in diametrically opposed, rearwardly angled external grooves 130, formed in the forepart of the bolt, of pins 132, working in longitudinal horizontal slots 134, formed in the sidewalls 136 of the magazine 14, the slots 134 being on a level coincident with the axis of the bolt 86. One of the pins 132 is provided with a laterally outwardly extending ngerpiece 138, which provides for manual shifting of the bolt 86, when desired.

The threaded boss 102 is removably threaded into a forwardly projecting socket 140 on the upper forward part of the receiver 12, concentric with the bore 88, so that the ride barrel 104 lies conformably in the longitudinal groove 142, formed in the top of the hollow wooden forepart 144, of the rifle stock. For the purpose of reinforcing land rigidifying the forepart 144, longitudinally spaced heavy rigid sheet metal or plastic, U- shaped braces 146 are countersunk in and firmly secured, as by cementing, in the sidewall 148 and the bottom wall 150 of the forepart 144.

Forward and rearward movements of the bolt 86, and cocking of the trigger hammer assembly 38, accompanied by the locking and unlocking rotation of the bolt, explained hereinabove, are produced by a gas-operated action, ygenerally designated 152 which is contained within the forepart 144, beneath the rie barrel 104.

The action 152 comprises a relatively large cross section, longitudinally elongated, horizontal gas cylinder block 154, which is suitably xed to the underside of the rie barrel 104, at a location spaced forwardly from the receiver 12, and extending, at its forward end, as far as the open forward end 156 of the stock forepart 144. The block 154 is formed with a chamber or bore 158, which opens to the rear end 158 of the block, and to the for- 4 ward end of the block, where the bore 158 is closed by a screw plug 160.

The cylinder block bore 158 has a relatively large diameter forward portion 162, and a relatively small diameter rear portion 164, and a free piston 166, shorter in length than the bore 158, Works mainly through the smaller diameter rear bore portion 164. A relatively small diameter combustion gas duct 168 leads from the rifle barrel bore into the larger diameter forward portion 162 of the cylinder block bore 158, at a location near to the forward end of the portion 162. Gas discharge ducts lead out of opposite sides of the rear bore portion 164, at locations near to the read end of the latter. The benefit obtained by enlarging the diameter of the forward portion 162 of the cylinder block bore 158 is that thereby more room is provided for the expansion of gas entering the bore 158, supplemented by the additional room for expansion provided in the bore 158 as the piston 166 is moved rearwardly by the presence of the gas, with the result that the piston travels rearwardly in a more gradual and gentle manner than would be the case with a uniform diameter bore 158. This results in substantial reduction of noise, knock, and wear in the action 152.

As shown in FIGURE 5, the piston 166 has on its forward end a relatively wide arcuate cross section plate 168', reaching at its sides beyond the sides of the riile barrel 104, for the purpose of obtaining a relatively large cross section bearing for making a more stable action of a rectangular slide 172, with whose forward side the plate 168 is secured. The slide is formed with an axial bore 174, receiving a slide rod 176.

The slide rod 176 has a reduced diameter terminal 178, on its forward end, which is threaded and shouldered, as indicated at 180, into a socket 182, in the forward side of the forward part 184, of the receiver 12, at a location spaced downwardly from the rifle barrel 104, and located in the vertical plane of the barrel. The upper end of a set screw 186 retainably engages the terminal 178, through a vertical bore 188 in the forward part 184, in which the screw is threaded, as indicated at 190, in FIGURE 3.

The forward end 192 of the slide rod 176, which is located beneath the forward end of the cylinder block 154, is formed with a threaded socket 194, into which is threaded a reduced diameter terminal 196 of a rifle barrel securing rod 198, which has a fixed hexagonal head 200, fixed on its forward end. A groove 202 extends around the forward end of the stock forepart 144, which has a continuation 204, in the forward end of the cylinder block 154, in which is removably engaged a rearwardly extending peripheral flange 206, of a barrel securing plate 208, which is centrally traversed by the securing rod 198, with the head 200 forcibly engaged with the forward surface of the plate. The rod 198 slides through an eye 199 on the underside of the block 154.

By means of this arrangement, rotating the head 200, in the proper direction, disconnects the securing rod 198, from the slide rod 176, and allows the securing plate 208 to be removed, from the rifle barrel 104 and the stock forepart 144, thereby freeing the barrel, along with the cylinder block 154, to be removed from the receiver 12, by unscrewing the barrel, for thorough breech cleaning of the barrel. Removal of the securing plate 208 also serves to expose the remaining component, of the action 152, for cleaning, inspection, and if necessary, replacement.

The slide 172 is of relatively large mass and cross section and is formed, around its rear side, with a circular peripheral flange 210, which forms a socket 212. Another socket 214, small enough in outside diameter to be received by the slide socket 212, is formed, on the forward side of the forward part 184 of the receiver 12, by an annular ange 216. An expanding coil return spring 218 is circumposed on the slide rod 176 and is compressed between the bottoms of the sockets 212 and 214. The spring 218 serves not only to cushion the rearward travel of the slide 172, as the rifle is iired, but to return the slide to its normal forward position, against the rear end of the cylinder block 154 and to return the piston 166 forwardly, `after a drive stroke.

A flat coil buffer spring 220 is secured around the annular flange 216, of the socket 214, which is adapted to be engaged by the ange 216 of the slide 172, toward the end of the rearward travel of the slide, whereby the shock, noise, and jar, which would otherwise occur as a result of forcible contact of the slide 172 with the receiver 12 are eliminated.

Cross pins 222 serve to fix securely to one side of the slide 172, the rear end of one of two ilat horizontal longitudinal action bars 224, which are adapted to move endwise in vertical slots 226, defined between the inner surfaces of the stock forepart sidewalls 148, and the related sides of the receiver 12, as shown in FIGURES 6, 7 and 8. The other action bar 224 is preferably integral with the related side of the slide 172. The action bars 224 terminate, at their rear ends, in upstanding right-triangular wings 228, having rearwardly and upwardly angled forward edges 230, which, as shown in FIGURE 1, are adapted to engage conformably angled top surfaces 232, formed on the forward part of the receiver, in the forward positions of the action bars. At their upper ends, the action bar wings 228 are operatively connected to the pins 132 which are engaged in the bolt rotating grooves 130, so that, as the slide 172 is moved rearwardly and forwardly, the bolt 86 is moved in corresponding directions, and rotated.

A safety feature concerning the bolt 86, involves forming the rear end of the bolt 86 with a substantially hemispherical cam surface 234, traversed by a normally vertical groove 236, in which the rear end 238, of a firing pin 240, is exposed, to be struck by the nose 48 of the hammer 40, when the trigger piece 74 is pulled. The groove 236 normally conformably receives the nose 48 of the hammer, but should the bolt 86 not be completely home, in its forward position, due to an incomplete rotation of the bolt, the groove 236 will be canted, relative to the nose 48 of the hammer, so that, if the trigger be pulled, the nose cannot enter the groove 236 and drive the tiring pin, but instead, engages the cam surface 234. This positively prevents disastrous firing or a chambered cartridge with the bolt not fully forward and locked. The ring pin 140 works in an axial bore 242, extending through the bolt 86, and is retained therein, and limited in movement, by the engagement of the tip 244 of a radial screw 246, in `a longitudinal groove 248, in the side of the firing pin, as shown in FIGURE 2.

What is claimed is:

l. The combination of a firearm receiver, a barrel extending forwardly from the receiver, said receiver being formed with bore means aligned with the barrel, the barrel being formed with a bore including a cartridge chamber, a cartridge detonating bolt movable endwise in the receiver bore means, a cylinder block secured to the underside of the barrel and spaced forwardly from the receiver, said block being formed with a rearwardly-opening bore containing an endwise movable piston, means providing communication between the barrel bore and the block bore in front of the piston, gas-discharge duct means leading from the block `bore adjacent to the rear end thereof, and means operatively-connecting the piston to the bolt, said connecting means comprising a slide bar affixed to and extending forwardly from the receiver, a slide circumposed on the slide bar and having a forward side adapted to be movably-engaged by the rear end of the piston, return-spring means compressed between the slide and the receiver, said block bore and the piston being of arcuate transverse cross section and relatively wide as compared to the slide bar.

2. A rearm comprising a receiver formed intermediate its ends with an upwardly-opening magazine, an upwardly spring-pressed cartridge follower in the magazine, said receiver having a rear part and a forward part, said rear part being hollow, a spring-pressed trigger hammer assembly mounted within said rear part of the receiver and having a trigger nger piece extending downwardly below said rear part, said assembly having an upstanding hammer formed with a forwardly-facing nose, said rear part of the receiver being formed with a rear horizontal bore overlying said assembly and opening at its forward end to the magazine, said forward part of the receiver being formed with a forward bore aligned with the rear bore, a bolt longer in length than the distance between the facing ends of said bores and adapted to bridge this distance when engaged in the forward bore in projected ring position, a barrel secured to and extending forwardly from the forward part of the receiver, said barrel having a bore smaller in diameter than and axially-aligned with said forward bore, the rear end of the barrel bore being formed with a shoulder cartridge chamber, said bolt having a longitudinally-movable firing pin having forward and rear ends, the rear end of the ring pin being adapted to be struck by the nose of the hammer as the result of pulling the trigger finger piece for ring a cartridge present in the cartridge chamber, a vertical downwardly springpressed safety bolt latch mounted at the rear end of the magazine and has a lower end exposed below the receiver in front of the trigger ngerpiece, said latch having a forwardly projecting shoulder at its upper end and said follower plate having a projection on its rear end adapted to engage beneath the shoulder, the lower end of the latch being adapted to be manually engaged and elevated to put an upper part of the latch in stop engagement with the forward end of the bolt in a retracted position of the bolt.

3. In combination, a rearm comprising a receiver, an open top magazine located intermediate the ends of the receiver and containing an upwardly spring-pressed follower plate, said magazine dividing the receiver into forward and rear parts, a gun barrel secured at its rear end to the forward part of the receiver and extending forwardly therefrom, said barrel being formed with a chambered bore, said forward and rear parts of the receiver being formed with aligned forward and rear bores which are aligned with the barrel bore, a bolt working in the receiver bores and adapted to be positioned in the rear bore in the retracted position of the bolt with its forward end at the rear end of the magazine, said bolt having a longitudinal-movable ring pin, a spring-pressed trigger hammer assembly on the rear part of the receiver, said assembly having a hammer formed with a nose adapted to strike the rear end of the ring pin for detonating a cartridge present in the chamber of the barrel bore, with the bolt in a forwardly-projected position, a hollow stock forepart beneath the barrel and extending forwardly from the forward part of the receiver, and a combustion gas-operated action enclosed within the stock forepart, said action comprising a cylinder block xed to the underside of the barrel, said block being formed with a bore opening to the rear end of the block and closed at its forward end, a piston working in the `block bore, a gas duct providing communication between the barrel bore and the block bore forwardly of the piston, gas-exhaust duct means leading out of the block bore at a location intermediate the ends thereof, drive means operativelyconnecting the piston to the bolt for moving the bolt rearwardly to a retracted position as the cartridge present in the barrel bore chamber is detonated, and spring-return means for returning said drive means and the bolt to forwardly-projected position, said stock forepart having an open forward end, said forward end being formed with a peripheral groove, the cylinder block having a forward end formed with a groove in continuation of the forepart groove, a securing yplate having a rearwardly extending kperipheral ange' engagedfin the forepart groove and the cylinder block groove, and a securing rod sliding through the securing plate and separably secured at its rear end to the forward end of the slide rod, and an enlarged head on the forward end of the securing rod bearing against'the yforward side of the securing plate.

4. A rearm comprising a receiver, an open-top magay zine located intermediate the endsof said receiver' and A dividing the receiver intor forward and rear parts, a gun f shock upon impact of said slide with ythe forepart of saidv barrel ysecured at its rear end to the forward part of the 1 receiver and extendingforwardly therefrom, saidbarrel f being formed with a chambered bore,` said forward and rear parts of the receiver being formed with aligned torward and rear bores which are aligned with the'barrely bore', a bolt working inthe receiver bores and adapted to be positioned'in the rear bore in the retracted position of the bolt with its forward end at the rear end of the maga'-k f zine, a hollow stock forepart provided with a closed end disposed beneath the barrel and extending forwardly from the forward part ofthe receiver, said :stock including any elongated cylindrical blockprovided with a bore extendworking in said bore, and a combustion gas-operated action arranged within said stock in cooperative relation `with respect to saidv cylinderblock, there being a gas duct providing communication between the barrel'bore and the block bore forwardly of the piston, gas-exhaust duct -means 'leading out of the vblock bore at a location be-y tween the endsof the piston, said action embodying a slide rod extendingflongitudinally otsaid stock forepart and located beneath said cylindrical block and having one end fxedly-supported in the closed end of said forepart stock and having the otherend ixedly-supported in the forward part of the receiver, a slide slidable on the slide rod and freely-engaging the adjacent endof said piston, and 'means operatively-connecting said slide to said bolt for retractiley movement of said bolt responsive to the backward movement of said piston.

5. The firearm according to claim 4 which includes 4 in addition spring means operatively-connected to said slide and said slide rod and serving to cause simultaneous f nected to said slide, and a pair of upstanding wings located projectile movement of saidbolt andk forward movement ofy said piston.

6. The firearm according to claim 5 which includes in addition buffer spring means operatively-connected tothe orepart of rsaid receiver and serving to counteract the receiver when the bolt has executed its retractile movement. v

7. The rearm according to claim 4 wherein said means comprises a partof flat horizontal longitudinal action bars having one of the coniplernental ends operatively-conadjacent to and attachedto the other of the complemental f ends of saidaction bar, said wings being operatively-coning axially 'therethrough and having an elongated pistonr f nected to a pair of pins riding in arcuate slots formed in l said bolt.

`8. The rearm according to claim 4 wherein said-y y block bore includes a rear bore portion and a forward bore portionwhich is of larger diameter thany the rear borey portion,y and wherein said piston works mainlyk through the smaller diameter rear bore portion. v

References Cited by the Examiner y y f yUNITED STATES PATENTS Al. l57 12/1856 Newton l2-2O 853,715 '5/1907 yMondragon 42-22 2,394,986y 2/1946 Crockett 89--193' 27,582,989 1/1952 Harvey 89-193 2,932,108' 4/196()r Hughel et al 89-185 3,009,396 l l/l961 Dixon 89'l 9'1 r3,058,399 10/1962 Allyn 89-'191 3,137,084 6/1964 Reed 42-25 3,161,978 12/1964 OBrien et al 42-25' FOREIGN PATENTS 652,962 5/1951 Great Britain. 321,532 10/1934 Italy.

SAMUEL FEINBERG, Primary Examiner. f f

FRED C. MATTERN, JR., Examiner.

S. C. BENTLEY, Assistant Examiner. 

4. A FIREARM COMPRISING A RECEIVER, AN OPEN-TOP MAGAZINE LOCATED INTERMEDIATE THE ENDS OF SAID RECEIVER AND DIVIDING THE RECEIVER INTO FORWARD AND REAR PARTS, A GUN BARREL SECURED AT ITS REAR END TO THE FORWARD PART OF THE RECEIVER AND EXTENDING FORWARDLY THEREFROM, SAID BARREL BEING FORMED WITH A CHAMBER BORE, SAID FORWARD AND REAR PARTS OF THE RECEIVER BEING FORMED WITH ALIGNED FORWARD REAR BORES WHICH ARE ALIGNED WITH THE BARREL BORE, A BOLT WORKING IN THE RECEIVER BORES AND ADAPTED TO BE POSITIONED IN THE REAR BORE IN THE RETRACTED POSITION OF THE BOLT WITH ITS FORWARD END AT THE REAR END OF THE MAGAZINE, A HOLLOW STOCK FOREPART PROVIDED WITH A CLOSED END DISPOSED BENEATH THE BARREL AND EXTENDING FORWARDLY FROM THE FORWARD PART OF THE RECEIVER, SAID STOCK INCLUDING AN ELONGATED CYLINDRICAL BLOCK PROVIDED WITH A BORE EXTENDING AXIALLY THERETHROUGH AND HAVING AN ELONGATED PISTON WORKING IN SAID BORE, AND A COMBUSTION GAS-OPERATED ACTION ARRANGED WITHIN SAID STOCK IN COOPERATIVE RELATION WITH RESPECT TO SAID CYLINDER BLOCK, THERE BEING A GAS DUCT PROVIDING COMMUNICATION BETWEEN THE BARREL BORE AND THE BLOCK BORE FORWARDLY OF THE PISTON, GAS-EXHAUST DUCT MEANS LEADING OUT OF THE BLOCK BORE AT A LOCATION BETWEEN THE ENDS OF THE PISTON, SAID ACTION EMBODYING A SLIDE ROD EXTENDING LONGITUDINALLY OFSAID STOCK FOREPART AND LOCATED BENEATH SAID CYLINDRICAL BLOCK AND HAVING ONE END FIXEDLY-SUPPORTED IN THE CLOSED END OF SAID FOREPART STOCK AND HAVING THE OTHER END FIXEDLY-SUPPORTED IN THE FORWARD PART OF THE RECEIVER, A SLIDE SLIDABLE ON THE SLIDE ROD AND FREELY-ENGAGING THE ADJACENT END OF SAID PISTON, AND MEANS OPERATIVELY-CONNECTING SAID SLIDE TO SAID BOLT FOR RETRACTILE MOVEMENT OF SAID BOLT RESPONSIVE TO THE BACKWARD MOVEMENT OF SAID PISTON. 